It is not used since commit 
0096420adb03 ("btrfs: do not
account global reserve in can_overcommit").
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
 
        return NULL;
 }
 
-static inline u64 calc_global_rsv_need_space(struct btrfs_block_rsv *global)
-{
-       return (global->size << 1);
-}
-
 static u64 calc_available_free_space(struct btrfs_fs_info *fs_info,
                          struct btrfs_space_info *space_info,
                          enum btrfs_reserve_flush_enum flush)